Test layers on one engine and share selection and shader helpers

Layer display tests no longer re-check Cesium primitives in every layer:
they run on the fake engine, and one Cesium translation check per ground
kind lives in the Cesium engine's ground tests. Their harnesses are shared,
and the fake-engine, Cesium-engine and flights tests that repeated the
contract suite are gone, 340 tests in all.

The press-travel measurement is shared by the selection dispatcher and
CCTV, which loses its ScreenSpaceEventHandler shim and world-click module.
ALPR, installations and bikeshare share one selection keeper and selected
marker write. Layers with their own click rules keep their handlers.

Navara's pulse is a class like the ground pass, the ground and imagery
passes share the surface uniforms, and the colour, log-depth and occlusion
GLSL lives in one chunk module, each caller keeping its depth bias. The
ground suite runs inside the contract suite (--only=ground:), and fixture
and script names say what they test.

Behaviour is unchanged on both engines.

scripts/qa-all-layer-switches.mjs

@@ -334,7 +334,7 @@ const runs = [
     ['--panoramax'],
   ],
   ['radio-engine-switch', 'radio-engine-switch', ['radio']],
-  ['w2-imagery', 'w2-imagery', ['recent-imagery']],
+  ['imagery-contract', 'imagery-contract', ['recent-imagery']],
   ['fire-camera-switch', 'fire-camera-switch', ['alpr-cameras']],
   [
     'fire-camera-switch--fires',